1. Technical Field
The present invention generally relates to acoustic transducers and manufacturing methods thereof. More particularly, the present invention relates to an interchangeable magnet and magnet assembly for loudspeakers, and methods for assembling loudspeakers utilizing the same.
2. Related Art
Loudspeakers are universally known and utilized in audio systems for the reproduction of sound. Essentially, loudspeakers are transducers which convert electrical energy to acoustic energy. There are a wide variety of designs employing various operational principles, and can be generally categorized as electrodynamic, electrostatic, piezoelectric, or discharge, among others.
The most common type of loudspeaker is of the electrodynamic variety, in which an electrical signal representative of the desired audio is applied to a voice coil wound around a bobbin and suspended between opposite poles of a magnet. The region between the poles is known as the air gap, and the magnetic field present therein interacts with the electrical current passed through the voice coil. The electromagnetic force moves the bobbin/voice coil along the air gap, and the displacement or movement thereof is controlled by the magnitude and direction of current in the coil and the resulting axial forces. The bobbin is also attached to a cone-shaped semi-rigid diaphragm, and the vibration of the bobbin is correspondingly transferred thereto. The base of the diaphragm is generally suspended from the rim of the loudspeaker basket, and provides lateral stability. The apex of the diaphragm generally includes a damper, also known in the art as a spider, a ring-shaped member having an interior edge that may be glued to the bobbin and an exterior edge that may be glued to the basket. The damper resiliently supports the bobbin at the respective predetermined static positions within the air gap without the voice coil contacting the surrounding surfaces of the yoke or the magnet.
A problem with conventional loudspeakers lies in the fact that the magnet used to generate the magnetic field can be susceptible to fracturing and breakage, such as when moving or transporting the loudspeaker, when the loudspeaker is exposed to extreme temperatures, or when the loudspeaker is operated at high power levels for excessively long periods of time. Breakage or fracturing of the magnet adversely affects the quality of sound generated by the loudspeaker by distorting the magnetic field generated by the magnet, and thus such damage to the magnet is, understandably, highly undesirable. Moreover, as it is typical in conventional loudspeakers to permanently affix the magnet to other components within the speaker frame, any repair of such conventional loudspeakers can require the complete disassembly of the loudspeaker, which is a labor-intensive process that often must be performed by a loudspeaker repair specialist. It is also not unusual for loudspeakers to have the magnet permanently affixed therein in a way that effectively eliminates options for repairing the loudspeaker. For example, disassembly of the loudspeaker may excessively damage other loudspeaker parts, or may be excessively labor intensive, such that the cost of the repair of the loudspeaker exceeds the overall replacement cost.
Yet another problem associated with many conventional loudspeakers is the generation of excessive levels of heat that can occur during operation thereof. The generation of heat can result from the application of electrical power to the voice coil, as a substantial portion of the electrical power is converted into heat, rather than sound. Excessive heat emitted from the voice coil can negatively impact the performance and longevity of the loudspeaker. For example, excessive heat can weaken the holding strength of adhesives used to attach pieces of the loudspeaker together, thereby structurally damaging the loudspeaker, and excessively high temperatures can even at least partially melt parts of the load speaker such as the wire insulation and other components. Excessive heat levels can even contribute to breakage of the loudspeaker magnet, for example by inducing excessive thermal expansion stresses in the magnet. The control of the heat generated during operation is so important for the optimal performance of the loudspeaker, that a factor typically used in industry to determine the power handling capacity of the speaker is in fact the ability of the device to tolerate heat. The heat tolerance of the speaker can be judged, for example, by the lowest melting point of the wire insulation and other components, as well as by the heat capabilities of the adhesive used to affix the coil.
Also, yet another effect that impairs performance of the speaker is the temperature induced resistance of the voice coil, also called the power compression of the voice coil. As the temperature of the voice coil rises, the DC resistance of the wire also increases. This resistance leads to a reduced efficiency for conversion of the received electrical signal to the acoustical output that becomes increasingly worse with increasing temperatures of the voice coil. Thus, as the voice coil becomes hotter, a higher voltage must be applied to achieve the same level of acoustic conversion, which higher voltage itself increases the temperature of the voice coil until a point is reached where further increases in the applied voltage results in virtually no increase in acoustical output and only a further increase in heat. The heating of the coil can thus produce undesirable non-linear loudness compression effects at high sound levels.
Various different methods have been attempted to provide “cooling” to the voice coil during operation of the loudspeaker, such as by venting the loudspeaker to provide a flow of air past the voice coil. Examples of such venting methods are described in U.S. Pat. No. 5,909,015 to Yamamoto et al, U.S. Pat. No. 6,219,431 to Proni and U.S. Pat. No. 6,390,231 to Howze, each of which is herein incorporated by reference in its entirety. For example, Yamamoto et al. describes a self-cooled loudspeaker having a permanent magnet assembly with a top plate stamped to form a plurality of intake and outtake air paths, where the movement of the diaphragm generates a unidirectional flow of air through the plurality of intake and outtake air paths. Proni describes a loudspeaker with a frame and motor structure, and a flow path in between the frame and top plate of the motor structure that directs air over at least a portion of the voice coil. Howze describes a loudspeaker having directed airflow cooling where an airflow director is provided to transfer heat away from a former to which the voice coil is attached.
However, a problem with such prior solutions is that they often do not provide adequate cooling of the voice coil and surrounding structures. For example, while venting may provide an initial release of hot air from the speaker, the hot air may also in certain instances be pulled back into the speaker, for example by movement of the diaphragm, such that operation of the loudspeaker for a sufficient duration merely results in the re-circulation of the hot air through the speaker. Also, vented loudspeakers may undesirably expose the interior of the loudspeaker to the surrounding environment, which exposure can introduce harmful particulate matter from the environment into the loudspeaker interior, as well as adversely affect the desired acoustic dynamics. For example, exposing the loudspeaker interior to the environment can attract magnetic particles into the interior of the speaker, which particles can interfere with the interaction of the magnet assembly and voice coil to distort the acoustic output.
Accordingly, there remains a need in the art for efficient and reliable means for effecting repair of loudspeakers having damaged magnets, such as methods and apparatus that allow for ready replacement of damaged magnets within a speaker. There further remains a need for an apparatus and method that provides for the control of temperatures within the loudspeaker in a manner that reduces heat damage incurred in components of the speaker, and which improves the acoustic performance of the speaker. There remains a further need in the art for an apparatus and method for controlling temperatures in the loudspeaker that does not require the presence of ports connecting the interior of the loudspeaker to the speaker exterior.